1. Filed of the Invention
The present invention relates to a particulate matter washing apparatus or method for washing contaminated particulate matter scraped up from filtering media in a filtering pond or from a bottom of a waste water pond or a sedimentation basin, etc., or surface-covering sand to remove muck on or materials covering the surface of the grains of the particulate matter.
2. Description of the Prior Art
Filtering sand used in a water purifying plant is collected from a river bottom or a river-mouth, but a quantity of the resource is limited, so that sand once used is again used after cleaning or other similar processing. In association with rapid contamination of resource water or under influence caused by contaminants flowing into a filtering pond, such phenomena have been observed as that a grain diameter of the filtering material has become larger due to deposition of sludge or that sludge is separated from the filtering media. When a grain diameter of filtering media becomes larger as described above, a space between the filtering media is reduced and the filtering efficiency becomes lower. So it is required to periodically take out the filtering media from the filtering pond and remove muck from a surface of the filtering media by means of washing.
Conventionally, in the processing for washing filtering media, generally there has been used a washing apparatus having agitation vanes to mix contaminated sand and cleaning water and agitate the mixture, but when a large quantity of contaminated sand is forcefully agitated, the sand grains are pulverized due to collision with the agitation vanes or friction between the filtering media themselves, and resultantly a portion which can not be recycled increases, and further if a quantity of cleaning water is small, the separated contaminants are again deposited on the sand grains, which makes it difficult for us to expect high efficiency in the processing for cleaning.
Also as the so-called washing apparatus for sand, there has been proposed an apparatus having a sand scrape-up section at a central position of the basic body for agitating and washing sand by making use of rotation of a screw conveyor provided in the sand scrape-up section. This sand washing apparatus is an apparatus used mainly for removing salt deposited on a surface of sea sand, and has the construction in which the screw conveyor has sand scrape-up vanes in its lower section and also agitation vanes on its upper section and blades for distribution are provided in the upper section of the sand scrape-up section.
In this type of sand washing apparatus as described above, sand put in a cleaning tank is raised due to effect by sand scrape-up vanes up to the agitation vane section, where the sand is mixed with cleaning water poured thereinto, the sand in the cleaning water is agitated, diluted, washed, and further raised upward by making use of rotation of agitation vanes, and then the sand is homogenized and forcefully moved from the sand scrape-up section to the cleaning tank. Because of this construction, it is required to inject sand into the cleaning tank up to at least a height of the blades for distribution, and further the cleaning water is supplied at a section where the agitation vanes rotate and salty water after cleaning is overflown from a water discharge pipe provided in the upper section of the cleaning tank, so that the cleaning tank is always required to be filled with the cleaning water.
As described above, generally the conventional type of sand washing apparatus has the configuration in which sea sand filling a tank is floated in and agitated with cleaning water to make salt deposited on a surface of sand grain dissolved in the cleaning water to acquire cleaned sand.
Even if filtering media is washed by using the conventional type of sand washing apparatus as described above, however, contaminants deposited on a gain surface are, different from salt, not dissolved into cleaning water, so that it has been impossible to expect a high cleaning effect. Also, when a supply rate of cleaning water is lowered to suppress floating of sand to be cleaned, as a large quantity of contaminated sand is forcefully agitated by the agitation vanes, which sometimes causes breakage pulverization of sand gains. Also as the sand scrape-up vanes and agitation vanes continue to rotate in the sand, so that friction between the agitation vanes and sand is disadvantageously large.
It is an object of the present invention to provide a sand washing apparatus which can effectively remove contaminants despited on and covering a surface of sand gain without pulverizing the injected sand and also in which wearing is generated little in the agitation member.